I have been looking into making a standard board for the $50 robot. ATMEGA328P with 16 powered I/O, both regulated and unregulated (selectable) with caps (470uf & 1000uf), all 6 ADC, and a current measuring point. it has no xtal... (too small)

The board size is 1.21" x 2.21" (3.1cm x 5.6cm)

to buy a whole kit, it costs just over £9 ($14.5)Thats the whole $50 robot MCU for $14.5